Rotor having longitudinal recesses in outer surface between V-slot poles

ABSTRACT

An electric motor includes a stator having a stator surface and a rotor rotatable relative to the stator. The rotor includes a plurality of poles, each of which is defined by a pair of magnets positioned in a V-shaped arrangement having a vertex positioned radially inward. The magnets present a mechanical pole angle of the corresponding pole. The rotor also includes a rotor surface that is opposite the stator surface. The rotor surface includes a plurality of circumferentially-spaced pole segments, each of which spans a respective mechanical pole angle. The rotor also includes a plurality of longitudinally extending recesses, each of which is positioned between adjacent pole segments.

CROSS-REFERENCE TO RELATED APPLICATION Priority Application

The present application claims priority from U.S. Provisional PatentApplication No. 62/614,148, filed Jan. 5, 2018, the entire disclosure ofwhich is hereby incorporated by reference herein.

Contemporaneously Filed Applications

The present application is filed contemporaneously with U.S. patentapplication Ser. No. 16/240,383, entitled ELECTRIC MOTOR WITH V-SLOTROTOR, filed Jan. 4, 2019, the entire disclosure of which is herebyincorporated by reference herein.

BACKGROUND

The embodiments described herein relate generally to electric motors,and more particularly, to electric motors including a v-slot rotor.

Permanent magnet rotors utilizing a V-slot design are known. The V-slotsfacilitate increasing a volume of magnets within a rotor pole. Thesedesigns are useful but typically result in increases in magnetic fluxleakage through the interpolar area between the magnets of adjacentpoles. A V-slot design also provides increased reluctance. While useful,there is a need for a rotor which provides a more constant power over awide speed range for a given motor size and configuration, which may bedictated by physical constraints placed on the motor.

SUMMARY

In one aspect, an electric motor is provided. The electric motorincludes a stator having a stator surface and a rotor rotatable relativeto the stator. The rotor includes a plurality of poles, each of which isdefined by a pair of magnets positioned in a V-shaped arrangement havinga vertex positioned radially inward. Each of the poles includes amechanical pole angle defined by the pair of magnets. The rotor alsoincludes a rotor surface opposite the stator surface. The rotor surfaceincludes a plurality of circumferentially-spaced pole segments, each ofwhich spans a respective mechanical pole angle. Moreover, the rotorincludes a plurality of longitudinally extending recesses defined in therotor surface. Each of the recesses is positioned between adjacent polesegments.

In another aspect, an electric motor is provided. The electric motorincludes a stator having a stator surface and a rotor rotatable relativeto the stator about an axis of the rotor. The rotor includes a pluralityof rotor poles, each of which is defined by a pair of magnets positionedat a mechanical pole angle relative to one another in a V-shapedarrangement. The rotor also includes a rotor surface opposite the statorsurface, with the rotor and stator surfaces defining an air gaptherebetween. The rotor surface has a rotor surface contour includingcircumferentially-alternating first and second segments, with each ofthe first segments spanning the mechanical pole angle of each respectiverotor pole. A first air gap distance is defined between the statorsurface and each of the first segments of the rotor surface contour, anda second air gap distance is defined between the stator surface and eachof the second segments of the rotor surface contour. The second air gapdistance is greater than the first air gap distance.

This summary is provided to introduce a selection of concepts in asimplified form. These concepts are further described below in thedetailed description of the preferred embodiments. This summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used to limit the scope of theclaimed subject matter.

Various other aspects and advantages of the present invention will beapparent from the following detailed description of the preferredembodiments and the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described in detail belowwith regard to the attached drawing figures, wherein:

FIG. 1 is a perspective of an exemplary electric motor constructed inaccordance with one embodiment of the invention;

FIG. 2 is an exploded perspective view of electric motor shown in FIG.1;

FIG. 3 is a cross-sectional view of the electric motor shown in FIGS. 1and 2, taken along line 3-3 of FIG. 1;

FIG. 4 is an enlarged cross-sectional view of the rotor of in theelectric motor shown in FIGS. 1 and 2, particularly illustrating alamination of the rotor core;

FIG. 5 is an enlarged view of a portion of the lamination shown in FIG.4, illustrating the configuration of one of the V-shaped magnet slotswith respect to a respective pole sector;

FIG. 6 is an enlarged cross-sectional view of a rotor core constructedin accordance with a second embodiment of the invention, particularlyillustrating an alternative laminated design; and

FIG. 7 is an enlarged view of a portion of the lamination shown in FIG.6, illustrating the configuration of one of the V-shaped magnet slotswith respect to a respective pole sector.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. While the drawings do notnecessarily provide exact dimensions or tolerances for the illustratedcomponents or structures, the drawings are to scale with respect to therelationships between the components of the structures illustrated inthe drawings.

DETAILED DESCRIPTION

The following detailed description of embodiments of the disclosurereferences the accompanying drawings. The embodiments are intended todescribe aspects of the disclosure in sufficient detail to enable thoseskilled in the art to practice the disclosure. Other embodiments can beutilized, and changes can be made without departing from the scope ofthe claims. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present disclosure isdefined only by the appended claims, along with the full scope ofequivalents to which such claims are entitled.

In this description, references to “one embodiment,” “an embodiment,” or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment,” “an embodiment,” or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will beclear to those skilled in the art from the description. For example, afeature, structure, act, etc. described in one embodiment may also beincluded in other embodiments but is not necessarily included. Thus, thepresent technology can include a variety of combinations and/orintegrations of the embodiments described herein.

In the following specification and the claims, reference will be made toseveral terms, which shall be defined to have the following meanings.The singular forms “a,” “an,” and “the” include plural references unlessthe context clearly dictates otherwise. “Optional” or “optionally” meansthat the subsequently described event or circumstance may or may notoccur, and that the description includes instances where the eventoccurs and instances where it does not.

As used herein, the terms “axial” and “axially” refer to directions andorientations extending substantially parallel to a longitudinal axis ofthe electric motor. The terms “radial” and “radially” refer todirections and orientations extending substantially perpendicular to thelongitudinal axis of the electric motor. In addition, as used herein,the terms “circumferential” and “circumferentially” refer to directionsand orientations extending arcuately about the longitudinal axis of theelectric motor. Moreover, directional references, such as, “top,”“bottom,” “front,” “back,” “side,” and similar terms are used hereinsolely for convenience and should be understood only in relation to eachother. For example, a component might in practice be oriented such thatfaces referred to herein as “top” and “bottom” are in practice sideways,angled, inverted, etc. relative to the chosen frame of reference.

In the exemplary embodiment, the electric motor 10 is illustrated as abrushless permanent magnet, inner rotor motor. As will be described, aninner rotor motor has magnets positioned radially-inward relative towindings, which act as the stator. However, according to some aspect ofthe present invention, the rotor may alternately be an outer rotor motoror dual rotor motor.

As shown in FIGS. 1-3, the illustrated electric motor 10 generallyincludes a stator assembly 12, a rotor assembly 14 supported forrotation relative to the stator assembly 12, a controller housing 16enclosing control electronics (not shown) for controlling operation ofthe electric motor 10, a housing 18 including a base portion 20 and anendshield 22, a first bearing assembly 32, and a second bearing assembly34. The base portion 20 of the housing 18 is generally cylindrical inshape and includes a closed end 36 proximate the first bearing assembly32 and an open end 38 opposite the closed end 36 for receiving at leasta portion of the stator assembly 12 and the rotor assembly 14. Theendshield 22 cooperates with the base portion 20 to substantially definea motor chamber in which the stator assembly 12 and the rotor assembly14 are at least substantially housed. The controller housing 16 iscoupled to the endshield 22 and encloses the control electronics andother various power and controller components of electric motor 10therein. While the illustrated embodiment is one configuration of theelectric motor 10, it is noted that electric motors of variousconfigurations are contemplated, including, for example, electric motorshaving vented or otherwise open motor housings or shells, etc.

In the exemplary embodiment, the closed end 36 of the base portion 20includes a first bearing support (not shown) sized and shaped to receiveand secure the first bearing assembly 32 therein. For example, andwithout limitation, the first bearing support may include a recessedportion defined in the closed end 36. Alternatively, the first bearingsupport may be any structure or component configured to receive andsecure the first bearing assembly 32 and that enables the electric motor10 to function as described herein.

The endshield 22 includes a second bearing support 40 defined thereinand positioned substantially in a center of the endshield 22 such thatit is aligned axially with the first bearing support and concentric withthe rotation axis “A.” The second bearing support 40 is sized and shapedto receive and secure the second bearing assembly 34 therein. Forexample, and without limitation, as shown in FIG. 1, the second bearingsupport 40 is a recessed portion or bearing cup defined in the endshield22. Alternatively, the second bearing support 40 is any structure orcomponent, such as an aperture, configured to receive and secure thesecond bearing assembly 34 and that enables the electric motor 10 tofunction as described herein.

The first bearing assembly 32 and the second bearing assembly 34 areconfigured to rotatably support the rotor assembly 14. In particular,the rotor assembly 14 preferably includes a rotor shaft 42 fixedlysupporting a rotor core 44 with the rotor shaft 42 extending axiallythrough each of the bearing assemblies 32 and 34. In the exemplaryembodiment, each of bearing assemblies 32 and 34 is a ball bearingassembly including a plurality of steel balls (not shown) positionedbetween outer races 46 a and 46 b and inner races 48 a and 48 b,respectively. The outer races 46 a and 46 b of the first and secondbearing assemblies 32 and 34 are fixedly coupled to the first and secondbearing supports, respectively. The inner races 48 a and 48 b arefixedly coupled to the rotor shaft 42 and are configured to rotaterelative to the outer races 46 a and 46 b via the interposed steelballs. In alternative embodiments, the first and second bearingassemblies can be any type of bearing and/or bearing assembly thatenables the electric motor 10 to function as described herein, such as,without limitation, sleeve bearings, plain bearings, fluid bearings,and/or active magnetic bearings.

As best shown in FIG. 3, in the exemplary embodiment, the statorassembly 12 is a three-phase stator assembly having twelve slots. Inaccordance with certain aspects of the present invention, the statorassembly 12 can alternatively be configured as a single phase ordifferent multi-phase motor and can have an alternative number of slots.In the exemplary embodiment, the stator assembly 12 is a segmentedstator that includes a plurality of stator segment assemblies 28combined to form the segmented stator assembly 12. Each of the statorsegment assemblies 28 includes a toothed core 26, axially-oppositeinsulators 30, and a winding 24. The windings 24 are configured to beelectrically energized to generate an electromagnetic field. Thewindings 24 are fabricated from wire (e.g., aluminum or copper) coiledor otherwise wound around the teether of the toothed core 26. Theinsulators 30 surround the toothed core 26 and are positioned betweenthe toothed core 26 and the windings 24 to facilitate electricalisolation of the winding 24 from the respective core 26. While thesegmented stator assembly 12 is illustrated for purposes of disclosure,it is contemplated that the electric motor 10 may include a statorassembly of various other configurations (e.g., an endless(non-segmented) toroidal core having alternative or no core insulation,etc.) and having different shapes.

In the exemplary embodiment, the toothed core 26 includes a solid core.A solid core can be a complete, one-piece component, or can includemultiple non-laminated sections coupled together to form a completesolid core. The toothed cores 26 may be formed, for example, and withoutlimitation, from a soft magnetic composite material, a soft magneticalloy material, and/or a powdered ferrite material. It is noted that theuse of soft magnetic composite materials and soft magnetic alloys in asolid core 26 facilitate 3-dimensional flux paths and facilitatereducing high frequency losses (e.g., losses at frequencies above sixty(60) Hz) when compared with laminated stator yokes. The use of softmagnetic composite materials and soft magnetic alloys also facilitatesincreasing the structural rigidity of the toothed cores 26, whichfacilitates improving performance and minimizing noise.

Alternatively, the toothed cores 26 may be formed from a stack oflaminations, or the cores may be integrally formed into an annular shapeand fabricated from a plurality of laminations in the form of platesstacked one on top of the other. For example, and without limitation, insuch a laminated structure, the laminations are stacked or placed inface-to-face contact such that the stack extends axially along therotation axis “A” a predetermined length. The plurality of laminationsmay be interlocked (i.e., coupled to each other) or loose laminations.The laminations are fabricated from a magnetically permeable material,such as, for example, a steel or a steel alloy. Additionally, in someembodiments, a laminated stator core may be skewed by angularlyoffsetting laminations. For example, the skewed design may involveangularly offsetting each lamination a given angle relative to theaxially adjacent lamination.

Each exemplary insulator 30 is fabricated from a thermoplastic syntheticresin suitable for use in the electric motor 10. For example, andwithout limitation, each insulator 30 may be fabricated by injectionmolding the resin into the shape of the insulator 30. However, it iscontemplated that the insulators 30 may be fabricated from anynon-conductive material that enables the insulators 30 to function asdescribed herein. Furthermore, the insulators 30 may be fabricated bymethods other than molding. For example, they may be fabricated bycoating the core or by machining. Each insulator 30 is positioned on arespective toothed core 26 and located between a corresponding winding24 and the respective core 26. Each insulator 30 may be formed from twoidentical components coupled together to form a substantially tubularshape that extends radially when positioned on cores 26. In addition,each insulator 30 is coupled to the corresponding core 26 such that theinsulator 30 covers the entirety of the radial surfaces of therespective core. That is, each preferred insulator 30 coverssubstantially the entire core 26 except for a radially inner end surfaceof the core.

In the exemplary embodiment, as described above, the rotor assembly 14includes the rotor core 44 coupled to the rotor shaft 42. The rotor core44 is substantially cylindrical in shape having an outside nominaldiameter D₁ smaller than an inside diameter D₂ of an inner surface 60 ofthe stator assembly 12. The difference between D₁ and D₂ defines a firstair gap, or basic air gap, of the electric motor 10. In the exemplaryembodiment, the rotor core 44 is a permanent-magnet rotor and includes aplurality of substantially rectangular permanent magnets 50.Alternatively, the rotor core 44 is any type of rotor that enables theelectric motor 10 to function as described herein. In the exemplaryembodiment, the rotor shaft 42 is fixedly coupled to the rotor core 44and positioned concentrically relative thereto so as to extend along therotation axis “A.” The rotor shaft 42 a first end 52 that extendsforward from the rotor core 44 and a shorter second end 54 that extendsrearward from the rotor core 44.

While the magnets 50 are describe above as being substantiallyrectangular, it is noted that alternative magnet shapes are within theambit of certain aspects of the present invention, as long as theangular relationships of each pole are maintained in accordance with theprinciples of the present inventions, as described below.

The rotor core 44 and the magnets 50 are configured to rotate with therotor shaft 42. In the exemplary embodiment, the rotor core 44 may befabricated from a plurality of laminations 56 (see FIG. 4) stacked orplaced in face-to-face contact such that the rotor core 44 extendsaxially along the rotation axis “A” a predetermined length. Theplurality of laminations 56 may be interlocked (i.e., coupled to eachother) or loose laminations. Alternatively, in some embodiments, therotor core 44 may be a solid core, formed without laminations.

In the exemplary embodiment, the rotor core 44 includes a plurality ofV-shaped magnet slots 58 extending through the rotor core 44,substantially parallel to the rotation axis “A.” The V-shaped magnetslots 58 are circumferentially positioned at substantially regularintervals about the rotation axis “A.” Each of the V-shaped magnet slots58 is configured to receive two of the magnets 50 therein to secure thepair of magnets 50 in a V-shaped arrangement. As will be described, eachV-shaped arrangement or V-shaped magnet slot 58 defines a magnetic poleof the rotor assembly 14, meaning the illustrated electric motor 10 is aten (10) pole motor. The illustrated embodiment includes ten (10)V-shaped magnet slots 58, thus defining ten (10) pole sectors 62. It isnoted that the rotor core 44 may include more or fewer pole segments,depending on the electric motor design requirements. It is also notedthat the magnets 50 are shown schematically for purposes of illustrationbut are generally sized to fit tightly within the V-shaped magnet slots58 to facilitate a secure, non-moving fit with the rotor core 44.Additionally, or alternatively, the magnets 50 may be secured in theV-shaped magnet slots 58 with adhesive, fasteners, etc.

FIG. 4 is an enlarged cross-sectional view of the rotor core 44,particularly illustrating one of the laminations 56. As described above,in the exemplary embodiment, the lamination 56 defines ten (10) polesectors 62. End portions 64 of each of the V-shaped magnet slots 58 arepositioned radially outward from the rotation axis “A” of the rotorassembly 14, which is shown as the center of the lamination 56. A vertex66 of each of the V-shaped magnet slots 58 is thus positioned radiallyinward. A plurality of radial pole pitch lines 100 extend through thecenter of the lamination 56 (i.e., rotation axis “A”), with each radialpole pitch line 100 being centered angularly between an adjacent pair ofthe V-shaped magnet slots 58 such that the adjacent pair of the V-shapedmagnet slots 58 are disposed symmetrically about the respective radialpole pitch line 100. Each radial pole pitch line 100 defines theboundary between two adjacent pole sectors 62, wherein adjacent radialpole pitch lines 100 define a pole sector 62. Each pole segment includesa central pole axis 102 that passes through the center of the lamination56 and bisects the respective pole sector 62 (i.e., is angularlycentered between adjacent radial pole pitch lines 100). In FIG. 4, onlythe vertical-most central pole axis 102 is shown for clarity.

As used herein, a pole pitch angle is defined as the angle betweenidentical points on two adjacent pole sectors 62. For example, andwithout limitation, a pole pitch angle 104 of the lamination 56 isillustrated in FIG. 4 as the angle between adjacent radial pole pitchlines 100, where the central pole axis 102 is positioned between theadjacent radial pole pitch lines 100 at an angle equal to one-half ofthe pole pitch angle 104. The pole pitch angle is determined by dividingthree hundred and sixty degrees (360°) (one full turn of the rotor) bythe number of pole sectors 62 of the rotor core 44. For example, in theexemplary embodiment, the ten (10) pole rotor core has a pole pitchangle 104 equal to thirty-six degrees (36°), i.e. three hundred andsixty degrees (360°) divided by ten (10) poles.

FIG. 5 is an enlarged view of a portion of the lamination 56 shown inFIG. 4, illustrating the configuration of a V-shaped magnet slot 58 withrespect to a respective pole sector 62. In the exemplary embodiment,radial lines 106 extend through the center of the lamination 56 (i.e.,rotation axis “A”), with each radial line 106 passing through aradially-outward, inwardly-facing corner of a respective magnet 50(inwardly facing refers to the inner portion of the V-shaped magnet slot58). The two respective lines 106 of a V-shaped magnet slot 58 define amechanical pole angle 108 of a pole 110 of the rotor assembly 14. Asused herein, the pole 110 is a magnetic pole of the rotor defined as theactive or effective magnet pole area of the V-shaped magnet arrangement.In the exemplary embodiment, the effective magnet pole area is equal toan arc or segment 112 (also referred to as a pole segment) of the rotorcore surface spanning the mechanical pole angle 108. As shown in FIG. 4,the central pole axis 102 bisects the mechanical pole angle 108 and theV-shaped magnet slot 58. That is, the vertex of the V-shaped magnet slot58 lies on the central pole axis 102, and the V-shaped magnet slot isdisposed such that it is symmetric with the central pole axis 102.

Referring to FIGS. 4 and 5, in the exemplary embodiment, the rotor core44, or the laminations 56 that make up a stacked rotor core 44, includesan outer surface contour 120. The outer surface contour 120 includes aplurality of circumferentially-alternating first and second segments 112and 114, respectively. The outer surface contour 120 defines a pluralityof axially extending recesses 116 (shown in FIG. 1) of the rotor core44. More particularly, each second segment 114 of the outer surfacecontour 120 defines one of the recesses 116. The first segments 112 arearcuate in shape (preferably extending along a common arc that definesthe rotor nominal outside diameter D₁), and each first segment 112 spansthe corresponding mechanical pole angle 108. The first segments 112 aresubstantially centered on the rotation axis “A” of the rotor assembly 14to define the nominal outside diameter D₁. As such, the first segments112 provide a substantially uniform air gap width W₁ between the innersurface 60 of the stator assembly 12 and the first segments 112. Thesecond segments 114 span the distance between adjacent first segments112. The second segments 114 are substantially the same in shape andform, being generally arcuately concave with respect to the innersurface 60 of the stator assembly 12. As such, the second segments 114provide a substantially non-uniform air gap between the inner surface 60of the stator assembly 12 and the second segments 114. Most preferably,the second segments 114 are each at least substantially centered on arespective radial pole pitch line 100 and are symmetric thereabout.

The non-uniform air gap varies from the air gap width W₁, correspondingto the intersection of one of the second segments 114 with one of thefirst segments 112 of the first pole 110, to a maximum air gap width ofW₂ (at a midpoint of the second segment 114) and back to the air gapwidth W₁, corresponding to the intersection of the second segment 114with an adjacent first segment 112 of an adjacent second pole 110. Thenon-uniform air gap width W₂ facilitates increasing the saliency of therotor assembly 14 by reducing flux leakage from the rotor assembly 14 tothe stator assembly 12 and increasing reluctance at the space betweenthe poles 110. In one suitable embodiment, the maximum distance thesecond segments 114 extend radially inward a distance of at leasttwo-hundredths of an inch (0.02″) relative to the first segments 112, asindicated by W₃.

In the exemplary embodiment, the mechanical pole angle 108 is in therange between about forty-seven percent (47%) and about fifty-threepercent (53%) of the pole pitch angle 104. In the illustratedembodiment, the rotor core 44 is a ten (10) pole rotor. As such, themechanical pole angle 108 is in the range between about seventeendegrees (17°) and about nineteen degrees (19°) for the ten pole rotor.This facilitates increasing the flux density within the span of themechanical pole angle 108, which has the effect of increasing the backelectromotive force (or “back emf”) of the electric motor 10 for thesame magnet volume. This back emf increase for the same magnet volumefacilitates generating more effective power from the electric motor 10.The non-uniform air gap width W₂ facilitates focusing the flux densitythrough the first segment 112 areas of the rotor core 44 defined by themechanical pole angle 108, which increases the operating efficiency andreducing current load of the electric motor 10.

The angles discussed above are geometric and are expressed as mechanicaldegrees. For the design of electric motors, electrical degrees are alsoemployed so that results can be generalized. It is noted that each polepitch angle (or pole sector 62) of the electric motor 10 is equal toone-hundred and eighty electrical degrees (180° electrical), as themagnetic poles are one-hundred and eighty electrical degrees (180°electrical) apart. An electrical degree is a unit of measurement of timeas applied to alternating current—one complete cycle equalsthree-hundred and sixty electrical degrees (360° electrical). Forexample, one cycle in a rotating electric motor is accomplished when therotating field moves from one pole to the next pole of the samepolarity. There are three-hundred and sixty electrical degrees (360°electrical) in this time period. Therefore, in a two (2) pole (one (1)pole pair) electric motor there are three-hundred and sixty electricaldegrees (360° electrical) in one revolution, and the electrical andmechanical degrees are equal. In a machine with more than two (2) poles,the number of electrical degrees per revolution is obtained bymultiplying the number of pole pairs by three hundred and sixty degrees(360°). Thus, in the exemplary embodiment, the electric motor 10includes ten (10) poles, or five (5) pole pairs and the number ofelectrical degrees is equal to one thousand and eight hundred (1800°electrical), i.e., five (5) pole pairs times three-hundred and sixtyelectrical degrees (360° electrical). As such, each mechanical degree ofrotation of the electric motor 10 is equal to five (5) electricaldegrees, i.e., one thousand and eight hundred (1800° electrical) dividedby three hundred and sixty degrees (360°).

As described above, the effective magnet pole area is equal to the arcor span of the segment 112. In the exemplary embodiment, the effectivemagnet pole area is in a range between and including about eighty-fiveelectrical degrees (85° electrical) and about ninety-five electricaldegrees (95° electrical), where the pole sector 62 spans one hundred andeighty electrical degrees (180° electrical). As such, the mechanicalpole angle 108 may be determined by the following equation:(360÷No. of rotor poles)×(effective magnet pole area÷180)Where “No. of rotor poles” equals the number of poles 110 (or polesectors 62) of the rotor core 44 and the “effective magnet pole area” isin the range of 85° electrical to 95° electrical. In the illustratedembodiment, the rotor core 44 is a ten (10) pole rotor. As such, themechanical pole angle 108 is in the range between and including aboutseventeen degrees (17°) and about nineteen degrees (19°). In otherwords, the most preferred mechanical pole angle 108 for the illustratedelectric motor 10 is about one-half (½) of three hundred and sixty (360)divided by ten (10) poles.

FIG. 6 is a schematic view of an alternative lamination 200 constructedin accordance with another embodiment of the present invention. In thissecond embodiment, the lamination 200 defines twenty-eight (28) polesectors 202, each of which includes a V-shaped magnet slot 204,substantially parallel to the rotation axis “A.” The V-shaped magnetslots 204 are circumferentially positioned at substantially regularintervals about the rotation axis “A.” Each of the V-shaped magnet slots204 is configured to receive two permanent magnets therein, such asmagnets 50 (not shown in FIG. 6). End portions 206 of each of theV-shaped magnet slots 204 are positioned radially outward from therotation axis “A.” A vertex 208 of each of the V-shaped magnet slots 204is thus positioned radially inward. A plurality of radial pole pitchlines 210 extend through the center of the lamination 200 (i.e.,rotation axis “A”), with each radial pole pitch line 100 being centeredangularly between an adjacent pair of the V-shaped magnet slots 204 suchthat the adjacent pair of the V-shaped magnet slots 204 are disposedsymmetrically about the respective radial pole pitch line 210. Eachradial pole pitch line 100 defines the boundary between two adjacentpole sectors 202, wherein adjacent radial pole pitch lines 210 define apole sector 202. Each pole segment includes a central pole axis 212(only one (1) shown in FIG. 6 for clarity) that passes through thecenter of the lamination 200 and bisects the respective pole sector 202(i.e., is angularly centered between adjacent radial pole pitch lines210).

FIG. 7 is an enlarged view of a portion of the lamination 200 shown inFIG. 6, illustrating the configuration of the V-shaped magnet slot 204with respect to a respective pole sector 202. A pole pitch angle 214 isas the angle between adjacent radial pole pitch lines 210, where thecentral pole axis 212 is positioned between the adjacent radial polepitch lines 210 at an angle equal to one-half of the pole pitch angle214.

In this second embodiment, the radial lines 216 extend through thecenter of the lamination 200, with each radial line 216 passing througha radially-outward, inwardly-facing corner of a respective magnet 50.The two respective lines 216 of a V-shaped magnet slot 204 define amechanical pole angle 218 of a pole 220. The central pole axis 212bisects the mechanical pole angle 218 and the V-shaped magnet slot 204.That is, the vertex 208 of the V-shaped magnet slot 204 lies on thecentral pole axis 212, and the V-shaped magnet slot is disposed suchthat it is symmetric with the central pole axis 212.

The lamination 200 includes an outer surface contour 222, which includesa plurality of circumferentially-alternating first and second segments224 and 226, respectively. The outer surface contour 222 defines aplurality of axially extending recesses, such as the recesses 116 (shownin FIG. 1), of the rotor core 44. More particularly, each second segment226 of the outer surface contour 222 defines one of the recesses 116.The first segments 224 are arcuate in shape (preferably extending alonga common arc that defines the rotor nominal outside diameter D₁), andeach first segment 224 spans the corresponding mechanical pole angle218. The first segments 224 are substantially centered on the rotationaxis “A” of the rotor assembly 14 to define the nominal outside diameterD₁. As such, the first segments 224 provide a substantially uniform airgap width W₄ between the inner surface 60 of the stator assembly 12 andthe first segments 224. The second segments 226 span the distancebetween adjacent first segments 224. The second segments 226 aresubstantially the same in shape and form. More specifically, each secondsegment 226 is generally V-shaped segment with respect to the innersurface 60 of the stator assembly 12. Each second segment 226 mostpreferably has a vertex 228 that is centered on a respective radial polepitch line 210.

Each of the magnets 50 present a generally flat, radially outer magnetend 230 opposite the vertex 228. Each of the V-shaped second segments226 include a first section 232 that is parallel to a magnet end 230 ofa first pole sector 202, and a second section 234 that is parallel to amagnet end 230 of an adjacent pole sector 202. The first and secondsections 232 and 234 are spaced a distance 236 from the respectivemagnet ends 230. In one preferable embodiment, the distance 236 is atleast twenty-five thousandths of an inch (0.025″), although othersuitable distances are within the ambit of certain aspects of thepresent invention.

The non-uniform air gap varies from the air gap width W₄, correspondingto the intersection of one of the second segments 226 with one of thefirst segments 224 of the first pole 220, to a maximum air gap width ofW₅ (at a midpoint of the second segment 226) and back to the air gapwidth W₄, corresponding to the intersection of the second segment 226with an adjacent first segment 224 of an adjacent second pole 220. Thenon-uniform air gap width W₄ facilitates increasing the saliency of therotor assembly 14 by reducing flux leakage from the rotor assembly 14 tothe stator assembly 12 and increasing reluctance at the space betweenthe poles 220. In one suitable embodiment, the second segments 226extend radially inward a distance of at least two-hundredths of an inch(0.02″) relative to the first segments 224.

An effective magnet pole area of each pole 220 is equal to the arc orspan of the first segment 224. In this second embodiment, the effectivemagnet pole area is in a range between and including about eighty-fiveelectrical degrees (85° electrical) and about ninety-five electricaldegrees (95° electrical), where the pole sector 202 spans one hundredand eighty electrical degrees (180° electrical). As such, the mechanicalpole angle 218 may be determined by the following equation:(360÷No. of rotor poles)×(effective magnet pole area÷180)Where “No. of rotor poles” equals the number of poles 220 (or polesectors 202) of the rotor core and the “effective magnet pole area” isin the range of 85° electrical to 95° electrical. In the illustratedembodiment, the rotor core is a twenty-eight (28) pole rotor. As such,the mechanical pole angle 218 is in the range between and includingabout six point one (6.1°) and about six point eight degrees (6.8°). Inother words, the most preferred mechanical pole angle 218 for thissecond embodiment of the electric motor 10 is about one-half (½) ofthree hundred and sixty (360) divided by twenty-eight (28) poles.

Described herein are embodiments of an electric motor with an improvedV-slot rotor having poles with a magnet angle producing more back emfper turn at lower flux density. The electric motor also includes rotorsurface enhancements that facilitate increasing flux density at therotor poles. One advantage of the disclosed electric motor includesimproving torque/amp linearity by almost 20+% at peak current levelsover typical known V-slot motors. The disclosed V-slot rotor has aneffective magnetic pole angle between eighty-five degrees electrical(85° electrical) to ninety-five degrees electrical (95° electrical),which is advantageous in that it facilitates increasing the volt/turnback emf. Another advantage is that the disclosure provides an electricmotor with increased motor efficiency and reduced current load.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, any featureof a drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the invention,including the best mode, and to enable any person skilled in the art topractice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

The invention claimed is:
 1. An electric motor comprising: a statorhaving a stator surface; and a rotor rotatable relative to the stator,the rotor including— a plurality of poles, each of which is defined by apair of magnets positioned in a V-shaped arrangement having a vertexpositioned radially inward, each of said poles including a mechanicalpole angle defined by the pair of magnets, a rotor surface opposite thestator surface, said rotor surface including a plurality ofcircumferentially-spaced pole segments, each of which spans a respectivemechanical pole angle, and a plurality of longitudinally extendingrecesses defined in the rotor surface, each of said recesses beingpositioned between adjacent pole segments, each of said recesses definedby a concave curve relative to the adjacent pole segments, each of saidrecesses extending radially inward a depth of at least 0.02 inchesrelative to the adjacent pole segments.
 2. The electric motor inaccordance with claim 1, each of said magnets presenting a generallyflat, radially outer magnet end opposite the vertex, said poles beingarranged so that adjacent first and second poles present a first magnetof the first pole and an adjacent second magnet of the second pole, eachof said recesses being V-shaped, with a first recess section beingparallel to the magnet end of the first magnet and a second recesssection being parallel to the magnet end of the second magnet.
 3. Theelectric motor in accordance with claim 2, each of said recessespresenting a radially inward recess vertex, said vertex being centeredbetween adjacent pole segments.
 4. The electric motor in accordance withclaim 2, each of the first and second recess sections being spaced fromthe respective magnet ends substantially the same distance.
 5. Theelectric motor in accordance with claim 4, said distance between each ofthe first and second recess sections and the respective magnet ends isat least 0.025 inches.
 6. The electric motor in accordance with claim 1,said rotor being formed from a plurality of laminations stacked in anaxial direction.
 7. The electric motor in accordance with claim 1, saidstator being formed from a plurality of laminations skewed relative toone another to form a skewed stack of laminations.
 8. An electric motorcomprising: a stator having a stator surface; a rotor rotatable relativeto the stator about an axis of the rotor, the rotor including— aplurality of rotor poles, each of which is defined by a pair of magnetspositioned at a mechanical pole angle relative to one another in aV-shaped arrangement, a rotor surface opposite the stator surface, withthe rotor and stator surfaces defining an air gap therebetween, saidrotor surface having a rotor surface contour includingcircumferentially-alternating first and second segments, with each ofthe first segments spanning the mechanical pole angle of each respectiverotor pole, a first air gap distance defined between the stator surfaceand each of the first segments of the rotor surface contour, and asecond air gap distance defined between the stator surface and each ofthe second segments of the rotor surface contour, said second air gapdistance being greater than the first air gap distance, each of saidfirst segments being defined by arcs centered on the axis of the rotorand having substantially identical radiuses, each of said secondsegments defined by a concave curve relative to the adjacent firstsegments, each of said second segments extending radially inward adistance of at least 0.02 inches relative to the first segments.
 9. Theelectric motor in accordance with claim 8, each V-shaped arrangement ofmagnets having a vertex positioned radially inward, each of said magnetspresenting a generally flat, radially outer magnet end opposite thevertex, said poles being arranged so that adjacent first and secondpoles present a first magnet of the first pole and an adjacent secondmagnet of the second pole, each of said second segments being V-shaped,with a first section of the second segment being parallel to the magnetend of the first magnet and a second section of the second segment beingparallel to the magnet end of the second magnet.
 10. The electric motorin accordance with claim 9, each of said second segments presenting aradially inward second segment vertex, said second segment vertex beingcentered between adjacent first segments.
 11. The electric motor inaccordance with claim 9, each of the first and second sections of thesecond segments being spaced from the respective magnet endssubstantially the same distance.
 12. The electric motor in accordancewith claim 11, said distance between each of the first and secondsections and the respective magnet ends is at least 0.025 inches. 13.The electric motor in accordance with claim 8, said rotor being formedfrom a plurality of laminations stacked in an axial direction.
 14. Theelectric motor in accordance with claim 8, said stator being formed froma plurality of laminations skewed relative to one another to form askewed stack of laminations.
 15. An electric motor comprising: a statorhaving a stator surface; and a rotor rotatable relative to the stator,the rotor including— a plurality of poles, each of which is defined by apair of magnets positioned in a V-shaped arrangement having a vertexpositioned radially inward, each of said poles including a mechanicalpole angle defined by the pair of magnets, a rotor surface opposite thestator surface, said rotor surface including a plurality ofcircumferentially-spaced pole segments, each of which spans a respectivemechanical pole angle, and a plurality of longitudinally extendingrecesses defined in the rotor surface, each of said recesses beingpositioned between adjacent pole segments, each of said magnetspresenting a generally flat, radially outer magnet end opposite thevertex, said poles being arranged so that adjacent first and secondpoles present a first magnet of the first pole and an adjacent secondmagnet of the second pole, each of said recesses being V-shaped, with afirst recess section being parallel to the magnet end of the firstmagnet and a second recess section being parallel to the magnet end ofthe second magnet, each of the first and second recess sections beingspaced from the respective magnet ends substantially the same distance,said distance between each of the first and second recess sections andthe respective magnet ends is at least 0.025 inches.
 16. The electricmotor in accordance with claim 15, each of said recesses presenting aradially inward recess vertex, said vertex being centered betweenadjacent pole segments.
 17. The electric motor in accordance with claim15, each of said recesses extending radially inward a depth of at least0.02 inches relative to the adjacent pole segments.
 18. The electricmotor in accordance with claim 15, said rotor being formed from aplurality of laminations stacked in an axial direction.
 19. The electricmotor in accordance with claim 15, said stator being formed from aplurality of laminations skewed relative to one another to form a skewedstack of laminations.